1. Field of the Invention
The present invention relates to an adhesive tape for electronic parts to be used as TAB tapes, adhesive tapes for fixing the leadframe or for adhering between parts around leadframes making up a semiconductor device, e.g., lead pins, semiconductor chip mounted substrates, heat spreader, semiconductors themselves.
2. Description of the Related Art
Conventionally, adhesive tapes for fixing a leadframe, TAB tapes, etc., are used as adhesive tapes for use in the interior of resin-molded type semiconductor devices. For example, the adhesive tapes for fixing a leadframe have been used to fix lead pins of the leadframe in order to enhance the efficiency for producing the leadframe itself and the whole semiconductor assembly stages. In general, a leadframe manufacturer tapes the leadframe, and brings it to a semiconductor manufacturer, at which a semiconductor chip is mounted thereon followed by molding the leadframe with a resin. For this reason, it has been required for the adhesive tapes for fixing the leadframe not only to possess general reliability in a level required for semiconductor and enough processability at the time of taping, but also to possess sufficient adhesive strength at room temperature immediately after taping and heat resistance enough for withstanding thermal process at the stages of assembling semiconductor devices.
Conventionally, the adhesive tapes for use in such an problems that the generated gas stains the lead to cause deterioration of the adhesive strength or causes generation of package crack, because of insufficient heat resistance. It is therefore required to develop adhesives for electronic parts having sufficient heat resistance and reliability and adhesive tapes for electronic parts using them.
The present inventors have solved before the above problems by inventing adhesive tapes using an adhesive containing a polyimide composed of repeating units represented by the below-described formulas (1a), (1b), (2a) and (2b). (Japanese Patent Application Laid-open Nos. 325533/1996 and 67559/1997).
These adhesive tapes however have other problems. For example, there is a problem of easily causing interfacial separation of the adhesive layer from the heat resistant film in the case that the adhesive layer is formed on the heat resisting film. In particular, the interfacial separation at high humidity and high temperature becomes a serious problems because of causing remarkable deterioration of reliability of semiconductor packages. Moreover, there is a problem because of requiring two stages for bonding that it is not possible to prevent shifting or distortion of the lead pins, because the resin bonded by the first bonding stage softens by heating during the second bonding stage.
A both-sided adhesive tape in which adhesive layers having each a different glass transition temperature are provided on both sides of an insulating base film has been proposed for dissolving the above described problems. However, the both-sided adhesive tape has a drawback of causing warp of the leadframe because of the difference of thermal expansion application include adhesive tapes applying on a support film of a polyimide film, etc., an adhesive comprising polyacrylonitrile, polyacrylate or a synthetic rubber resin such as acrylonitrile-butadiene copolymer solely, or modified with any other resin or blended with any other resin to come into a B-stage. Both-sided adhesive tapes using thermoplastic polyimide resin having high reliability and high heat resistance have been utilized recently.
In recent years, resin-molded type semiconductor devices (semiconductor packages) as shown in FIGS. 1-3 have been developed and produced. In FIG. 1, the device has a construction in which lead pins 3 and metal plane 2 are connected by means of an adhesive layer 6, a semiconductor chip 1 is mounted on the metal plane 2, and bonding wires 4 between the semiconductor chip 1 and the lead pins 3, they are molded with a resin 5. In FIG. 2, the device has a construction in which the lead pins 3 and the semiconductor chip 1 are connected by means of an adhesive layer 6 and they are molded with a resin 5. In FIG. 3, the device has a construction in which the semiconductor chip 1 is mounted on a die pad 7, electrodes 8 and the die pad are connected by means of the adhesive layers 6, the semiconductor chip 1 is electrically connected to the electrodes 8 and the electrodes 8 are electrically connected to the lead pins 3 by means of bonding wires 4, and they are molded with a resin 5. In these cases, in general, single-layer adhesive tapes or both-sided adhesive tapes are used for the adhesive layer 6.
In the adhesive layers in the resin-molded type semiconductor devices shown in FIGS. 1-3, the use of an adhesive tape to which a conventional adhesive is applied has the between resins on both sides. Further, in the case of an adhesive tape consisting only of an adhesive layer, there is the problem that insulation becomes difficult to assure when the tape is bonded under pressure with heat, because the leadframe is embedded in and pierces the adhesive layer.
When an adhesive having a low glass transition temperature is used for satisfying the requirement for bonding at a lower temperature, adhesive strength at a high temperature becomes difficult to assure.
Japanese Patent Application Laid-open No. 40931/1997 discloses a varnish comprising a polyimide composed of 2,2-bisphthalic hexafluoroisopropylidene dianhydride, 4,4'-diamino-3,3',5,5'-tetraisopropyldiphenyl methane and siloxanediamine, to which a silane coupling agent is added. Since this adhesive is not the tape but is varnish, patterning on the chip is required and consequently the production processes becomes complicated. Moreover, there is a problem that poor wire-bonding is easily caused because of having no base film.
The present invention has been made for the purpose of solving such problems in the prior arts. Namely, an object of the present invention is to provide an adhesive tape for electronic parts capable of adhesion at a relatively low temperature without causing interfacial separation, with keeping electrical insulation and having sufficient reliability.